Question 1

Both primary and secondary active transport require the expenditure of metabolic energy.

Accepted Answer

Both primary and secondary active transport require the expenditure of metabolic energy, typically in the form of ATP. In primary active transport, energy is directly used to move molecules against their concentration gradient, while in secondary active transport, energy is indirectly used to move molecules using the electrochemical gradient established by primary active transport.

Question 2

In the body, Na+ ions behave as if they are nonpenetrating solutes because they are actively transported out of cells.

Accepted Answer

Na+ ions are actively transported out of cells through the sodium-potassium pump, which requires energy in the form of ATP. As a result, Na+ ions cannot freely move across cell membranes and behave as nonpenetrating solutes.

Question 3

Mediated transport is required in order for glucose, amino acids, and fatty acids to pass into cells because none of these substances can diffuse through plasma membranes.

Accepted Answer

This statement is false. Glucose, amino acids, and fatty acids can actually diffuse through plasma membranes, but mediated transport allows for more efficient and regulated transport of these substances into cells.

Question 4

The concentration of calcium in the cytosol of most resting cells is very much lower than the concentration of extracellular calcium.

Accepted Answer

The concentration of calcium in the cytosol of most resting cells is typically around 100 nM, while the concentration of extracellular calcium is around 1-2 mM, making it much higher than in the cytosol.

Question 5

Although permeability to mineral ions does not vary much from one cell to another, different cells vary considerably in their permeability to nonpolar molecules.

Accepted Answer

The answer of Although permeability to mineral ions does not...

Question 6

The final equilibrium state reached by a molecule that enters a cell by facilitated diffusion is the same as that for a molecule that enters the cell by diffusion.

Accepted Answer

Facilitated diffusion still relies on the concentration gradient and does not involve any active transport processes, therefore, the final equilibrium state will be the same as that for simple diffusion.

Question 7

Because of the active transport of Na⁺ and K⁺, the intracellular concentration of Na⁺ is lower than the extracellular concentration, whereas the reverse is true for K⁺.

Accepted Answer

Active transport moves Na⁺ out of the cell, leading to a lower intracellular concentration than extracellular concentration. However, active transport moves K⁺ into the cell, leading to a higher intracellular concentration than extracellular concentration.

Question 8

Active transport, facilitated diffusion, and osmosis all directly require the expenditure of metabolic energy.

Accepted Answer

Active transport requires energy to move substances against their concentration gradient, while facilitated diffusion and osmosis do not require direct energy expenditure, as they move substances along their concentration gradient.

Question 9

Adding one mole of NaCl to one liter of water will lower the water concentration twice as much as adding one mole of glucose.

Accepted Answer

This is because NaCl dissociates into two ions (Na+ and Cl-) when dissolved in water, while glucose does not dissociate. Therefore, adding one mole of NaCl will result in two moles of particles in solution, while adding one mole of glucose will result in only one mole of particles in solution. This means that adding one mole of NaCl will have a greater impact on the concentration of water molecules in solution.

Question 10

The Na/K ATPase pump is an enzyme that phosphorylates itself.

Accepted Answer

The Na/K ATPase pump is an enzyme that uses ATP to transport Na+ and K+ ions across the cell membrane. During this process, the enzyme undergoes phosphorylation, where it transfers a phosphate group from ATP to itself. This allows the enzyme to change shape and transport the ions across the membrane.

Question 11

The intracellular concentration of water in the cells of the body is normally the same as the extracellular concentration of water.

Accepted Answer

The intracellular and extracellular concentrations of water are typically in equilibrium to maintain osmotic balance across cell membranes.

Question 12

Specific proteins in the membranes mediate movement of lipid-soluble molecules into cells.

Accepted Answer

Lipid-soluble molecules typically pass through cell membranes by simple diffusion and do not require specific proteins to mediate their movement.

Question 13

In most of the cells in the body there is an electrical difference such that the inside of cells is positive with respect to the outside.

Accepted Answer

In most cells, the inside is negatively charged relative to the outside due to the distribution of ions across the cell membrane, primarily through the action of ion pumps and channels.

Question 14

In active transport, the affinity of any given binding site for the molecule to be transported changes as the site goes from facing one side of the membrane to facing the other side.

Accepted Answer

This is because active transport involves the use of energy to move molecules against their concentration gradient, and this energy is often used to change the shape or affinity of binding sites in order to move the molecule across the membrane.

Question 15

Integral membrane proteins can form channels through which ions such as Na+ and K+ can diffuse.

Accepted Answer

Integral membrane proteins serve as channels for ion diffusion, allowing the passage of ions such as Na+ and K+ through the cell membrane.

Question 16

The higher the osmolarity of a solution, the higher the concentration of water in it.

Accepted Answer

The higher the osmolarity of a solution, the lower the concentration of water in it. High osmolarity means there are more solutes in the solution, which means there is less room for water. Therefore, the concentration of water decreases as the osmolarity increases.

Question 17

Adding one gram of NaCl to one liter of water will lower the water concentration twice as much as adding one gram of glucose.

Accepted Answer

NaCl dissociates into two ions (Na+ and Cl-) when dissolved in water, effectively doubling the number of particles in solution compared to glucose, which does not dissociate. This increases the solute concentration more significantly with NaCl, affecting properties like osmotic pressure and freezing point depression more than glucose would, but it does not "lower the water concentration" in the manner suggested by the question. The concept of "lowering water concentration" is more accurately described in terms of increasing solute concentration, which affects the solution's properties differently than simply halving the water concentration.

Question 18

The Na+/K+-ATPase carrier transports sodium ions out of cells and potassium ions into cells on a one-to-one basis.

Accepted Answer

The Na⁺-K⁺-ATPase carrier typically transports 3 sodium ions out of the cell and 2 potassium ions into the cell, not on a one-to-one basis.

Question 19

The component of the plasma membrane that acts as a selective barrier to diffusion of polar molecules is the integral proteins.

Accepted Answer

The component of the plasma membrane that acts as a selective barrier to diffusion of polar molecules is the phospholipid bilayer, which consists of both hydrophilic and hydrophobic regions. Integral proteins can assist in transporting certain substances across the membrane, but they do not directly act as a selective barrier.

Question 20

If a cell were placed in a solution of 0.15 M NaCl, it would shrink.

Accepted Answer

The answer of If a cell were placed in a...

Quiz 4: Movement of Molecules Across Cell Membranes